A growing number of adolescents are being diagnosed with acute myocarditis following mRNA COVID-19 vaccinations. This case describes an adolescent who presented to the emergency department with chest pain and tachycardia following the Pfizer-BioNTech COVID-19 vaccination. Point-of-care ultrasound was performed prior to the return of laboratory studies and revealed depressed left ventricular systolic function. Point-of-care ultrasound may be a tool used to rapidly diagnose or risk stratify patients with potential post–COVID-19 vaccine myocarditis.